In this photo taken on Sept. 14, 2012, South Korean rapper PSY performs his massive K-pop hit "Gangnam Style" live on NBC's "Today" show in New York.The Associated Press

If nothing else, 2012 has proved the phenomenon of viral videos has become less about accidental fame on YouTube and more about marketing success. Nine of this year's top 10 trending videos on the popular video sharing site were created by professional producers.

"There are more and more people who know how to build an audience, how to use YouTube," YouTube trends manager Kevin Allocca told The Wall Street Journal. "There are companies who spend millions and millions of dollars trying to do create these videos."

It pays off, too. PSY's viral hit "Gangnam Style" has earned the South Korean rapper nearly $1 million just from YouTube this year. Other videos aim to spark discussion or reaction like Invisible Children's controversial "Stop Kony" campaign and "A Dramatic Surprise," a clever foreign ad for television network TNT.

And there appears to be no sign of slowing down. According to YouTube, more than 4 billion hours of videos are watched on the Google-owned site each month.

Here are YouTube Rewind's top 10 trending videos of 2012:

1. PSY - "Gangnam Style" (강남스타일)
Park Jae-sang's infectious pony-riding dance surpassed Justin Bieber this year to become the most viewed YouTube video of all time with 971 million views -- and counting.

2. Walk Off The Earth covers "Somebody That I Used to Know" by GotyeFive people using one guitar made an interesting rendition of 2012's most surprising hit song, racking up 140 million views in the process.

3. "KONY 2012"
A lengthy video at 31 minutes long, this campaign aiming to end Ugandan conflict set a record with more than 30 million viewers in a single day in March.

4. "Call Me Maybe" by Carly Rae Jepsen feat. Justin Bieber, Selena, more
The Canadian singer's hit song got a popularity injection from other singers that were already hot on the video-sharing website.

5. Barack Obama vs Mitt Romney: Epic Rap Battles Of History Season 2
Popular YouTube series "Epic Rap Battles" has made a name for itself with unlikely pairings (such as Mario Bros. vs. The Wright Brothers and Doc Brown vs. Doctor Who), but the presidential election made this obvious matchup poised for success.

6. "A Dramatic Surprise on a Quiet Square"
A mysterious button (no, not the "That Was Easy" button) in the middle of a Flemish town square adds drama if pushed, with hilarious results.

7. "Why You Asking All Them Questions?" #FCHW
Kosher and Spoken Reasons evaluate relationship questions with a comedic rap.

8. Lindsey Stirling's dubstep violin song "Crystallize"
Some would argue 2012 was the year of dubstep, and this unlikely genre mashup scored 38 million views since February.

9. Facebook Parenting: For the troubled teen
One father responds to his daughter's Facebook rant by reading her post on video and then shooting her laptop with a gun.

10. Mission highlights from Felix Baumgartner's supersonic freefall
On YouTube alone, more than 8 million viewers watched the live stream of this 24-mile skydive that broke the sound barrier.

YouTube also released a compilation Rewind video that looks at 2012 month-by-month with an interactive timeline including such highlights as the Tupac hologram, various lipdubs, and the Overly Attached Girlfriend meme: